1. The Field of the Invention
The present invention relates generally to orthopedic surgical devices, and more particularly, but not necessarily entirely, to a device and method for balancing flexion and extension gaps in total knee replacement surgery, and for preparing the knee joint, to receive an implant.
2. Description of Related Art
The knee joint is comprised essentially of four bones, the fibula, the tibia, the femur, and the patella or knee cap. The two major bones, namely the proximal portion of the tibia and the distal portion of the femur, articulate with one another forming the main articulation surface of the knee joint. More specifically, articulation between each condyle of the distal femur and the corresponding meniscus and condyle of the proximal tibia permits positioning of a patient's leg in both flexion and extension.
When a knee joint is damaged such that total knee arthroplasty (TKA) is required, resection of the proximal portion of the tibia and the distal portion of the femur is required to form an extension gap between said proximal portion of the tibia and said distal portion of the femur when the patient's leg is in full extension. Additionally, a posterior resection of the distal femur is required to form a flexion gap between said proximal portion of the tibia and said distal portion of the femur when the patient's leg is in full flexion. In creating the extension and flexion gaps it is advantageous to resect the bones in such a manner so as to form equivalent rectangular gaps between the proximal portion of the tibia and the distal portion of the femur when the patient's leg is fully extended and flexed. In other words, each gap may be defined by cuts made in the proximal tibia and the distal femur that are substantially parallel to one another creating two rectangular gaps that are substantially equivalent. It will be appreciated that a width of the extension gap may be substantially equivalent to a width of the flexion gap. These substantially equivalent rectangular gaps aid in creating the balance in the knee that will ultimately allow the patient to both fully flex and extend the leg.
In classic technique knee surgeries, the first portion of the surgery is usually the same, which essentially requires a surgeon to prepare the knee joint in a manner so as to create the extension gap. The extension gap may be formed by making a distal cut in the femur using a distal cut guide to prepare the femur for further operative steps. It will be appreciated that this first portion of the surgery comprises several individual steps, which will be expounded upon hereinafter in more detail. Each step aids in the placement of the distal cut guide on the distal femur to create an accurate distal cut. The next portion of the surgery comprises making a proximal cut on the tibia after which the challenge becomes to create substantially equivalent rectangular extension and flexion gaps. It will be appreciated that additional surgical steps must be taken to implant the artificial knee joint and to complete the surgery, which steps will not be fully addressed herein.
It will be appreciated that in classic technique knee surgeries, used to balance and prepare the knee joint to receive the prosthetic knee implant, the major steps of the procedure include the following: First, the distal femur is cut at a valgus angle, which is defined as the angle between the neutral mechanical axis of the limb and the anatomical axis of the femur, consistent with the valgus angle of the patient. Second, the proximal tibia is cut substantially perpendicular to the long axis of the tibia. Third, the ligaments are balanced while the knee joint is in extension so that there is a substantially rectangular extension space or gap. Fourth, the femur is sized based on the anterior and posterior dimensions of the distal femur using an A/P sizing guide. The A/P sizing guide is placed on the distal femur by inserting two pins into the distal femur, attaching the A/P sizing guide to the distal femur. Fifth, the A/P sizing guide is removed from the pins, and an A/P cutting block is then positioned over the pins and onto the distal femur. Sixth, the posterior cut is made in the distal femur, and the A/P cutting block and the pins are removed from the bone. Seventh, a spacer block is used to determine the equality of the flexion and extension gaps. Eighth, the remaining cuts are finished, and then a trial reduction is performed.
It will be appreciated that the above surgical procedure is merely one example of the many techniques that have been used in the orthopedic industry for knee replacement surgeries. It will be further appreciated that the above surgical procedure is not meant to be exhaustive, or even a summary, of the many surgical techniques that are used in the orthopedic industry to perform total knee replacement surgeries.
With many of the prior art knee balancing devices used in total knee replacement surgeries, positioning of the knee balancing device depends entirely on the placement of the pins in the distal femur. Such pin placement requires great precision in order to properly place and locate the knee balancing device on the femur. If the pins are not properly placed, the device will be mal-aligned on the distal femur. The surgeon must then remove at least one of the pins from the distal femur, and re-secure the at least one pin to the bone for another attempt at securing the knee balancing device to the bone in an aligned position, which drastically increases the time and difficulty of the surgery. The prior art knee balancing devices may also lead to over resection of the bones in the knee joint, as substantially equivalent rectangular gaps are sought, which may potentially cause problems if a later revision surgery becomes necessary.
Attempts have been made in the prior art to provide a device and method for locating the A/P cutting guide on the distal femur such that the device may be correctly placed and located on the distal femur initially, without the necessity of removing the device and re-pinning the device to the bone. For example, U.S. Pat. No. 5,364,401 (granted Nov. 15, 1994 to Ferrante et al.) discloses a system for resecting the distal femur where various devices can be sequentially placed on a base member having a pair of connected brackets that are axially and radially adjustable after being initially positioned on the bone. During a final stage of bone preparation, the system utilizes a cutting block that may be adjusted relative to its base. This device is characterized by several disadvantages, including the need to connect a complex series of brackets to a base creating a scaffolding to which several devices may be removably attached.
U.S. Pat. No. 5,830,216 (granted Nov. 3, 1998 to Insall et al.) discloses a set of instruments for orientation of the femoral implant, including an epicondylar guide configured for referencing external rotation from the epicondyles. The Insall et al. patent further discloses a posterior reference/rotation guide that can be attached to the epicondylar guide for checking the rotation relative to the intact posterior condyles to confirm the epicondylar setting, and an A/P cutting guide comprising a fin that is designed to fit into a slot cut in the distal femur so as to fix external rotation. The A/P cutting guide can only move in the anterior and posterior directions for making adjustments in the flexion and extension gaps. This device is disadvantageous because there is no mechanism for adjusting the rotation of the A/P cutting guide, making each step in the surgery crucial, leaving little to no room for human error.
The present invention is directed to an orthopedic device for flexion and extension balancing in the knee joint by creating substantially equivalent rectangular flexion and extension gaps between the patient's proximal tibia and distal femur. It is noteworthy that none of the prior art known to applicants provides an A/P cutting guide device that is easy to operate, has few component parts and a relatively low profile, and that may be adjusted (i) translationally, in the anterior and posterior directions relative to at least one pin placed in the distal femur, and (ii) rotationally, relative to the at least one pin placed in the distal femur, to which the A/P cutting guide may be attached.
The prior art is thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
The features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention without undue experimentation. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out herein and in the appended claims.